Diabetes is one of the most common chronic disorders, in which high blood glucose levels result from a lack of insulin production and/or insulin sensitivity. Individuals with high blood glucose metabolize more glucose via a glucose to sorbitol to fructose pathway in insulin insensitive cells such as lenses, peripheral nerves and glomerulus. This leads to an overabundance of sorbitol in the cells, which is not easily diffused through the cell membrane. The increased concentration of sorbitol triggers an influx of water into the cells, causing swelling and potential damage.
Aldose reductase, an enzyme present in many parts of the body, catalyzes the reduction of glucose to sorbitol, one of the steps in the sorbitol pathway that is responsible for fructose formation from glucose. Aldose reductase activity increases as the glucose concentration rises in diabetic conditions where tissues are no longer insulin sensitive. These tissues include, for example, lenses, peripheral nerves and glomerulus of the kidney. Sorbitol cannot easily diffuse through cell membranes and therefore accumulates, causing osmotic damage, which in turn leads to retinopathy, neuropathy, and nephropathy. Therefore, inhibition of aldose reductase could prevent the buildup of sorbitol in insulin insensitive cells in diabetics, and presents a novel method to prevent the macrovascular and microvascular complications in diabetic patients. In addition, aldose reductase inhibitors, such as zopolrestat, may aid in treating or ameliorating such effects and have shown efficacy in wound healing in the corneal epithelium of diabetic animal models.